The present invention relates to measurement methods and apparatus for taking ratios, and more particularly to a method and apparatus for determining the ratio of miles travelled to fuel consumed, hereinafter called the fuel consumption ratio, for an automobile or the like.
Many operators of motor-driven vehicles are interested in fuel economy, and make it a practice to calculate the fuel consumption ratio as an indication of the efficiency of the vehicle. Further, the fuel consumption ratio is obviously related to the driving habits of the operator and the condition of the vehicle. For this reason, many operators employ a fuel consumption ratio indicator as an aid to efficient operation of the vehicle.
In the prior art, many devices have been provided for measuring and indicating the fuel consumption ratio of a vehicle and, in general, have been directed to continuously operating systems which provide an instantaneous value of the ratio. For example, one typical device, shown in U.S. Pat. No. 2,803,400, functions to continuously measure the distance travelled per unit of time and the quantity of fuel consumed per unit of time, thereby providing two variable rates. The device continually divides one rate by the other to derive an instantaneous quotient which is then displayed as the fuel consumption ratio. Systems of this general type tend to vary only in the methods utilized to obtain the variable rates for the distance travelled and the fuel consumed and to derive the instantaneous quotient.
The problem with such devices is that the indications provided fluctuate extensively during operation due to the fact that the fuel consumption ratio parameter is a quotient derived from variable parameters which can vary widely for a particular vehicle, depending upon the environment and manner of operation. For example, the fuel consumed during the given time period is determined by a number of variables among which are speed, rate of acceleration, atmospheric conditions, the terrain over which the vehicle is travelling, and the manner in which the vehicle is operated. Small changes in any of these variables can cause corresponding changes in the fuel consumed and when taken in combination can cause wide changes in the amount of fuel consumed under different operating conditions.
The distance travelled during the given time period parameter, while relatively more stable than the fuel consumed parameter, is also affected by speed, rate of acceleration, and, to some degree, the manner in which the vehicle is operated. Again, changes in these variables cause corresponding changes in the distance travelled parameter.
Since the fuel consumption ratio is a quotient derived from the distance and fuel parameters, it can be seen that small changes in any of the above-mentioned variables can cause disproportionate changes therein. Thus, while displaying the instantaneous value of a parameter is useful when the parameter is relatively stable or changes at a slowly varying rate, the use of such a continuously operating system for providing an instantaneous value of the fuel consumption ratio, which is rapidly changing, results in a widely fluctuating indication of the ratio. These fluctuations can be annoying to a vehicle operator, who must divert attention from vehicle operation to the fluctuating indicator to derive any meaningful data, concerning the fuel consumption ratio, which will aid in more efficiently operating the vehicle, such as reducing speed, foregoing rapid accelerations and similar fuel saving methods that can be instituted by a change in vehicle operation.
In recognition of the above-mentioned problem, several prior art devices have been directed to systems for providing a relatively stable indication of the instantaneous value of the fuel consumption ratio. For example, one method, as shown in U.S. Pat. No. 3,379,055, that has been used to overcome the widely fluctuating indication is to provide the indicator with a brake which is used to hold the indicator in a steady position during the time required for consumption of a preselected quantity of fuel, after which time the brake is released momentarily to allow the indicator to provide a new reading. While preventing the continuous fluctuation of the indicator, this method still results in wide fluctuations of the indicator during the interval the indicator brake is released. Again, these fluctuations divert the attention of the vehicle operator from operation of the vehicle.
Another prior art system, shown in U.S. Pat. No. 3,405,554, overcomes the difficulty in reading the widely fluctuating variations in the fuel consumption ratio indication by plotting separate indications, for the distance and fuel consumed measurements, on a two dimensional scale, whereby one measurement indication establishes a location on the scale in one dimension while the other measurement indication establishes a location in the other dimension, thereby providing two values which, taken jointly, indicate the fuel consumption ratio. While providing easily read indications of the fluctuating measurements, this system requires that the vehicle operator integrate the two indications to derive any data meaningful to aid in efficient operation of the vehicle, again diverting attention from vehicle operation.
Thus, to use the fuel consumption ratio indicators heretofore provided, as an aid to efficient vehicle operation, the operator must divide his attention between operating the vehicle and monitoring the fuel consumption ratio indication. This would reasonably explain why such systems have not found wider usage.
To overcome the disadvantages in the prior art, it is a feature of the present invention to provide a stable indication of the fuel consumption ratio which may be utilized by the vehicle operator as an aid to more efficient operation of the vehicle and which does not detract the operator's attention from vehicle operation.
Another feature of the invention is to provide an improved method and apparatus for obtaining the fuel consumption ratio whereby a distance measurement is made during the period of time a vehicle operates on a preselected quantity of fuel, thereby averaging the ratio over the time period.
A further feature of the invention is to provide a continuous display of the ratio whereby the vehicle operator is not required to repeatedly monitor the display to obtain useful fuel consumption data.